block: make barrier completion more robust

[deliverable/linux.git] / block / elevator.c

diff --git a/block/elevator.c b/block/elevator.c
index 86836dd179c05476078719869a0481777e999bc1..261ffaaf47bdbd125e3c91e44a4e9f7b3ed59fc0 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -944,10 +944,14 @@ void elv_completed_request(struct request_queue *q, struct request *rq)
         * drained for flush sequence.
         */
        if (unlikely(q->ordseq)) {
-               struct request *first_rq = list_entry_rq(q->queue_head.next);
-               if (q->in_flight == 0 &&
+               struct request *next = NULL;
+
+               if (!list_empty(&q->queue_head))
+                       next = list_entry_rq(q->queue_head.next);
+
+               if (!q->in_flight &&
                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
-                   blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
+                   (!next || blk_ordered_req_seq(next) > QUEUE_ORDSEQ_DRAIN)) {
                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
                        blk_start_queueing(q);
                }